The present invention relates to information recording disks such as an optical disk, and more particularly to an optical disk according to a novel method of dividing a recording region into parts and of forming a header-signal generating pre-pit train.
An optical disk of the modified constant angular velocity (MCAV) type has been proposed which is higher in recording density than an optical disk of the constant angular velocity (CAV) type.
In the optical disk of the MCAV type, a ring-shaped recording region is divided in radial directions into a plurality of concentric, annular blocks, each of the blocks being divided in a circumferential direction into a plurality of equal sectors so that the number of sectors included in the outermost block is about twice as large as the number of sectors included in the innermost block and sectors included in all the blocks have substantially the same length, and a pit train for generating a header signal is previously formed in each sector at a fixed pit pitch.
When this optical disk is rotated at a constant angular velocity, and an appropriate clock frequency is used for each block, a linear recording density can be made constant in the whole of the recording region extending from the inner circumference thereof to the outer circumference (refer to a Japanese Patent Application JP-A-62-80,865).